Field of the Invention
The present invention relates to a machine tool having a warming-up function, and specifically, relates to a machine tool controlling warm-up operation on the basis of external factors such as atmospheric temperature and atmospheric humidity.
Description of the Related Art
A machine tool machines a workpiece by operating rotation drive means such as a spindle motor, in a situation where heat is generated from the rotation drive means itself or portions operating with the rotation drive means. Therefore, when the machining is started without preparation in the state where the machine tool is still cold, thermal displacement on the shafts and the like arises in response to temperature elevation caused by the generated heat. Thus, displacement in relative position between the workpiece and a tool arises, which problematically causes deterioration of machining precision.
A typical technique to handle such deterioration of machining precision due to the thermal displacement is warm-up operation. In the warm-up operation, an idle operation is performed in advance until the temperature of a machine tool saturates, before starting actual machining work, when power supply of the machine tool is turned on. Machining of a workpiece is not started until thermal displacement in portions such as a spindle is stabilized by the warm-up operation, as a result, the machining precision can be stabilized. As conventional technologies of machine tools performing such warm-up operation, for example, techniques disclosed in Japanese Patent Application Laid-Open No. 61-065735, Japanese Patent Application Laid-Open No. 2009-113138, Japanese Patent Application Laid-Open No. 2013-163255, and so on are proposed.
In view of scheduling of machining, warm-up operation of machine tools is desirable to be performed within a predetermined minimum necessary time. Nevertheless, the time of warm-up operation required for saturation of the temperature of the machine tool problematically changes depending on external factors such as atmospheric temperature in the place where the machine tool is installed.
In such an environment where the atmospheric temperature changes, when a technology on the warm-up operation of machine tools which executes a single warm-up operation program for a certain period, for example, as disclosed in Japanese Patent Application Laid-Open No. 61-065735, is applied, the time required for warm-up operation is set. However, this disadvantageously results in excess warm-up operation in case where, for example, atmospheric temperature is high. Moreover, according to technologies on warm-up operation of machine tools as disclosed in Japanese Patent Application Laid-Open No. 2009-113138 and Japanese Patent Application Laid-Open No. 2013-163255, a technique of continuously measuring the thermal displacement in a machine tool to determine whether to continue the warm-up operation can be adopted. Although such a technique can execute control so as not to perform an excess warm-up operation, how long the warm-up operation has to be performed is not apparent when the warm-up operation is started. Hence, an operator cannot predict the end time of the warm-up operation.